A power device, an electric power tool and a system. The power device (1) can provide power to various types of tool main bodies (2). The tool main body (2) comprises tool control unit. The power device (1) and the tool main body (2) are detachably connected. The power device (1) comprises power control unit used to control an operation of a motor (13). When the power device (1) is adopted by one tool main body (2), the power control unit receives a control command transmitted from the tool control unit, and controls, according to the control command, the motor (13) to operate. The power device (1) receives various types of battery packs (3) for power supply. The power control unit receives a control command transmitted from the battery pack (3) and controls, according to the control command, the motor (13) to operate.